In the container industry, in general, and in the food container industry, in particular, it is desirable to produce containers having a bottom profile that imparts strength to the container. Typically, these profiles include one or more annular rings or recesses formed in the bottom of the container to improve the buckling strength of the container.
Early presses formed such profiles by preforming the profile in a first station by pressing the material against a die having a profile pad that defines the desired profile. After preforming, the container was then moved to a second station either in the same press or a separate press, where the container is hit again to “reform” or deepen the profile to its final depth. By transferring the container from the first station to the second station, tension within the side walls created during the reform operation is relieved. In other words, during the reforming or resetting of the bottom profile, it is desirable to minimize the distance that the metal has to be pulled from the side wall to finally form the bottom profile. In this way, the severe stresses in forming a final profile in one stoke are relieved avoiding damage to the container that would cause it to be scrapped. While the two station method is effective in minimzing the stresses of forming a profile, based on this method's disadvantages of having to handle the container two times and the additional time needed to transfer the container between stations, presses have been developed to perform the preform and reform steps in a single press.
In one example in the industry, the press includes a punch assembly and die assembly located axially opposite of each other, where the punch assembly descends to first blank the material and then wipe the material over the outer perimeter of the die assembly to form an inverted container. As the inverted container is completed, the core of the punch contacts the core of the die to impart an initial profile to the bottom of the container. The core of the punch continues downward drawing the container inside out to form an upright container. At the bottom of the punch core's stroke, both the punch core and die core bottom out causing the punch core to press the material into a profile pad carried on the die assembly to impart the finished profile to the bottom of the container.
A pressure cylinder is formed beneath the profile pad such that the descending blow of the punch builds pressure behind the pressure pad causing it to fire upward as the punch assembly is withdrawn. It has been discovered that the pressure created behind the profile pad causes it to overtake the punch as it is withdrawn causing the profile to be too deep. As will be appreciated, given the small thicknesses involved, such deepening can significantly weaken the container. In some cases, this may lead to the bottom of the container being torn out during subsequent processing or in use. Consequently, a need exists in the art for a press for forming a container with a bottom profile that selectively controls movement of the profile pad up and down through movement of a die core riser up and down for the profile pad to selectively form the bottom profile in the container in cooperation with the punch.
It has also been found that in operating prior presses for forming containers with profiled bottoms, the tooling, and, particularly, the profile pad or the profile pad and the punch and the redraw die or the redraw die and the pressure sleeve, expand, as the press heats up. This expansion causes the tolerances between the punch and the profile pad, the pressure sleeve and the redraw die to fall outside of specification, which often results in variations in the height of the bottom profile and the height of the sidewall of the container. One variation that can occur is a deepening of the bottom profile and the sidewall. As will be appreciated, such a deepening can result in a weakened container that must be scrapped. Consequently, a need exists in the art for a press for forming a container with a bottom profile that has one or more biasing members that accommodate expansion in certain tooling components during operation of the press.
It has also been found that operators of presses for forming containers with profiled bottoms had to remove tooling components from a bottom surface of a fixed base of the press. As can be appreciated, a mechanic had to climb under the press in order to remove certain tooling components in an inefficient, potentially hazardous and time consuming process. Consequently, a need exists in the art for a press for forming a container with a bottom profile that allows for the simplified removal of a tool pack of tool components located within a part of the fixed base wherein the tool pack is removable from a top surface of the base.
It has also been found that in operating prior presses for forming containers with profiled bottoms, the tooling, and, particularly, the punch and the profile pad can impart a deepened profile in the container. As will be appreciated, such deepening can result in a weakened container that must be scrapped. Consequently, a need exists in the art for a press for forming a container with a bottom profile that has a punch and a profile pad with an annular projection or an annular shoulder wherein the projection and the shoulder clamp material between the projection and the shoulder and allow the material to roll up a preselected height into the container to form the bottom profile of the container.